Method of preparing bituminous road surfacing materials



y 1933- F. o. w. Looms ET AL ,91 ,761

METHOD OF PREPARING BITUMINOUS ROAD SURFACING MATERIALS Filed June 5,1931 WWWWp.

INVENTORS FREDERICK.0.W.LOOMIS DANIEL.M.LOOMI$ BY 3% ATTORNEY l atentedMay 30, 1933 units stares rREiiERIcK osoAR WARREN LOOMIS ANDzoAmnnmacxaY LOOMIS, or mou'rmiug e QUEBEC, CANADA Emmi) F, PREPARINGiar'ruminous moe i vi This'invention relates to the preparation of ro'adsurfacing materials and particularlyto the coating and mixing of themineral partieles'of the aggregate.-

T preparing road surfacing materials in accordance with-prevailingmethods wherein the bitumen is used in the form of a wateryemulsi'on;the-crushed stone or similar aggregateis initiallyplaced in a mixer andagi tated to efi'ect the desired distribution of the particles of varyingsizes. The bituminous emulsion is'then'added and the mixing operation'continued to distribute the bitumen. The'mixing is usuallycarried out in a pug mill or similar mixer equipped with revolv ingblades or in a revolvin drum which may or'ma'y-not be equipped withmixing blades. Genemny speaking, these and similar methods ofmixing nowin use arenot suitably adap'te'dto the use of bituminous emul-"si'o'nsiand do not produce satisfactory'resultsP When a pug mill orbladed mixer is used the pugging-jor blading action causes ail-immediatebreaking down of the emulsion. whichint'erfe'res with properdistribution of thebit-umen and produces a dry appearing mix ofunsatisfactory characteristics. In some instances the line particles ofthe aggregate may absorb and break down the emulsion by capillary actionand this also produces a detective dry appearing mix containin balls ofbitumen. In other instances wlgere the aggregate used is of a compositenature, including, for example, coarse particles of crushed stone andline particles of sand, there is a differential selection by the bitumenwhich generally leaves the sand uncoated. In an effort to avoid thesedifiiculties'it has been a practice to leave out the fines and to carryout the mixing operation in a rotary drum without the use of mixingblades. This produces a defective mix in thatthe coating of bitumencovering the mineral particles lacks stability and adhesiveness.

The improved method provided in accordance with this invention overcomesthese difficulties and enable bituminous emulsions to be successfullyused in the production of a 50 satisfactory mix in which the bitumen isunif IApphfcati on fi1ed .l'une 3, 1931,"Seria1 N 5. 54 11537? and iiimagnet 54, ies'il formly distributed over the surfaces of the. coatedparticles and possesses" the' desired qualifications with respect to"stability" and In accordance {winters iire'ferred mthod of carrying ibt ithe' iiivenfion "the aggregate is' initially separated into Genet andt e particles; the besistastier-r teseparation iscanaied but beingdependent upbntli n a' tu're ofthe aggi ate and the' ty'pe of mix to (sobe produced EA tertheseparatioii theooarse particle's ai fed 1 at 1 auniform rate into a revolving -'d'riim' preferably, equipped withsuitable 'lilades arranged so that the tense? particles are givenarolliii "and rota I shown diagrammatically in accompanying drawingfwherein Figure 1 is aview of the apparatus in side elevation, a part ofthemixing drum being broken away to disclose themeans provided forspraying the bituminous emulsion and the finer particles ofthe'aggregate onto the coarser particles/ v Y Figure 2 is a transversesectional view through the mixing drum illustrating diagrammatically themanner in Whichthe bi- 9o tuminous emulsion is sprayed 'onto the coarseparticles of the a gregate. In-this view the means provided %or sprayingthe" finer 'particles of the aggregate are omitted.

Figure 3 is a cross sectional View through the drum illustrating themanner in which the finer particles of the aggregate are sprayed ontothe coated coarse particles;

The initial separation of the aggregate v may be regulated to give anydesired ratio :to

of coarse to fine particles. Generally speaking, the separation shouldyield 70% to 90% of the aggregate as coarse particles and the remainderas fines. In one instance the aggregate used consisted of all sizes ofparint." This aggregate was separated; .into

coarse particles of a size exceeding 4. tin? and fine particles of asize less than A in.

This basis'bfs'epalation usually affords 75% to 80% coarse particles and157 .,When,nsing anuapparatus such as shown inQthe present drawing thecoarse particles resulting from. the initial separation are placed in astorage bin 5 equipped with a 29-. discharge controlling gate 6.whilethe fine particles are placed in -a similar. discharge bin-.7;equipped witha controlling gate 8; The coarse particles are deliveredfrom thebin; 5 ,tothe hopper 10 of a mechanical ;,feieder }whieh isherein .shown as .including anendless conveyor 11 driven by a beltconnection 12 fromamain drive shaft 13. The conveyor 11 functions. to vdeliver the coarse particles, at a uniform rate, to the feed hop- 0per:14;of a revolving drum 15 ,whichis preferably equippedwithmixingblades .16. As herein .shown .the drum is provided with annular trackmembers 17 mounted on supporting rollers 18 so that the drum has a,-.slight downward inclination towards 1 the discharge opening which islocated at the end remote from the feed hopper 14. The drum supportingrollers ;18 are carried by suitableshafts l9 and oneor both of these 4oshaftsfmay 'be driven from a motor 20 through any suitable form ofgearing such as that indicatedat 21. During rotation of the drum thecoarse particles progress towards the discharge end by a spiral motionin the, course of which the various surfaces of the particles areexposed to the action of the spraying devices 22 which are supplied withbituminous emulsion through a supplyfpipe 23 connected to the dischargeside of a suitable pump 24 which is also driven by a belt 25 from themain drive shaft 13. The pump is equipped with an intake pipe 24a and afunnel 246. The bitumen is delivered to the funnel through 5 a supplypipe 240 equipped with a valve 24d the, apparatus.

from the bin 7 into a feed hopper 26 and from thence onto the receivingend of a belt conveyor 27 having its discharge end located within thedrum 15. The conveyor 27 delivers the fine particles through a chute 28into t e. path. of .a blast of air coming from an. air nozzle 29,connected to the discharge side of a blower 30 which is driven by abelt "connection 31 from the main drive shaft 13. From-i'thedisclosures; of Figures ll and' 3' *it' will be noted that the fineparticles are sprayed onto the coarse articlesafter the lattr have'beenpassed" 'eneaththe spray devices 22,and coated ,with the bituminousemulsion." After" the spraying' ofthe finer particles the resulting; mixissubjected to a fewrevolutions of the drum. before passing outwardlythro ugh the discharge opening; at the lower endof-the drum, Tl1e..conveyor 27. is driven from the shaft l3 through the be t se n e e i3. a e -sea e 1131 4.

and .35..

. Wh aia ngiaea i 11 ftens i afa l 19f Zips-in length is 'i'evolved at.a speed :of approximately.

revolutions per minute the c oarse. particles will traverse thelengthofthedrum in about. 1 mins. Such a drum 1 will handle from 8 to12tons.of;coarse particles per hour; When using a drum of this characterthe bituminous emulsion is, usually pum'ped or otherwise supplied; tothe; spray nozzles 22 ata uniform rate of about- 8Q to 1 2O1g allonsper. hour.

such asemployed in connection with paint sprays or may be simply fprcedthrough the nozzlev openings by'pressure gas in the case of water spraynozzles. Generally speaking,

it is advisable to provide a number of: re

atively small sprays 22 in preferencegto a single large spray since thisenables the sprays to be distributed over a greater area and insuresthat each coarse particle is com-- ening the coarse or lineparticles-with water before feeding the same into the drum may beresorted to in order to eliminate differential selection by thebituminous emulsion and to ensure uniform coating of all particles.

The method of operation described in the foregoing may be readilyaltered or controlled to adapt the same to the use of p The emulsionmay-be, sprayedthr ough the nozzles: by the use ofiair or steam Thefiner particles of the aggre gate are preferably delivered into the mixsermondifi'erent aggregates and bituminous emulsions and to producevarious types of finished mixes. For example, bituminous emulsions whichare very sensitive to vibrations may be used by reducing the speed ofthe drum Whereas the breaking down of more stable emulsions aftercontact with the coarse particles may be readily accomplished ticles inplace thereon.

by accelerating the speed of the drum. Uniform distribution of thebitumen and fine particles in the mix may be obtained by regulating thesprays.

By completely eliminating the fine particles of the aggregate andtreating the coarse particles with kerosene or oil, either separately orcombined or accompanied by fine material such as hydrated lime, stonedust, etc., before spraying the coarser particles with the bituminousemulsion, a fairly satisfactory material is also produced in accordancewith this invention. This material may be improved by steaming the sameafter the application of the bituminous emulsion. Kerosene, oils orother substances may also be added to the bituminous emulsion before thelatter is sprayed onto the coarser particles in order to ensuresatisfactory results when the coarse particles are porous or dirty. Whenthe aggregate consists of glassy and dust free stone satisfactoryresults have been obtained by merely directing streams of bitumen ontothe particles instead of employing the sprays previously describedsince, in this case, the fine spraying of the bitumen is not alwaysnecessary.

From the foregoing it will be apparent that the method described hereincomprises the following essential steps: (1) separating the aggregateinto coarse and fine particles; (2) uniformly coating the coarseparticles with bitumen preferably applied in the form of a spray; and(3) spraying the coated coarse particles with the fine particles toretain the bitumen coating of the coarse par- In this process thedividing point between the coarse and fine particles of the aggregate ispredetermined so that none of the coarse particles are fine enough tocause the bitumen to congeal, set or break when sprayed thereon. At thesame time these coarse particles are small enough to prevent unduerunning off of the bitumen from the surfaces to which it is applied. Thedistribution and atomization of the sprays is regulated so that thecoarse particles are provided with a uniform bitumen coating of therequired thickness. Atomization of the bitumen may be effected byplacing the bitumen under the required pressure or by the use ofcompressed air, steam or any other means capable of close regulation. Bysuitably regulating the spraying of the fine particles of the aggregateit is possible to congeal,

s'tlt, or; :breakithe, bitumen or .bituminoius emulsion :j ust:sufficiently topreserve the uniformityof;the finishedimixiwithoutdestroy ing the plasticity necessary messytransportatiomandjlayingiof'tlie-mixn -.T!i"f Having thus described ourinvention,- whatawezclaimiisrf 1. A methodino'fapreparing' bituminousroad surfacing materials which comprises applying a coating ofbituminous emulsion to coarse aggregate particles of such size as toprevent breaking or excessive running off of the emulsion when appliedto said particles and then applying fines to the bituminous coatings ofthe coarse particles with sufficient impact to cause the bitumen of theemulsion to separate out and adhere to the coarse particles.

2. A method of preparing bituminous road surfacing materials whichcomprises (1) coating coarse particles of an aggregate with a bituminousemulsion applied in the form of a spray while subjecting the particlesto gentle agitation suflicient to cause all surfaces of the particles tobe exposed to the coating action of the spray, the size of saidparticles being predetermined to prevent breaking or excessive runningoff of the emulsion as it is applied to said particles and (2) thensubjecting the coated coarse particles to a spray of finer particlesdirected thereon with sufiicient force to break down the emulsion byimpact so that the bitumen of the emulsion is caused to separate out andadhere to the coarse particles to provide the latter with a uniformbitumen coating stabilized by incorporation of the fine particlestherein.

3. A method of preparing bituminous road surfacing materials whichcomprises (1) separating from an aggregate the finer particles whichwould tend to break down a bituminous emulsion applied to said aggregate(2) coating the remaining coarse particles of the aggregate with abituminous emulsion and (3) applying the finer aggregate particles ofthe initial separation to the coated coarse particles with sufiicientimpact to cause the bitumen of the emulsion to separate out and adhereto the coarse particles.

4. A method of preparing bituminous road surfacing materials whichcomprises (1) removing from an aggregate the finer particles which wouldtend to break down a bituminous emulsion applied to said aggregate (2)coating the remaining coarse particles of the aggregate with abituminous emulsion applied in the form of a spray while subjecting saidparticles to gentle agitation sufficient to cause all surfaces of theparticles to be exposed to the coating action of the spray and (3) thenspraying the finer aggregate particles of the initial separation ontothe"dated'coars?pai-ticles"wivith siifli v cient impact to caus thebitumdm 'of thw j emulsion tos'eparate'dut and adhere fid=th Icoarseparticles. 1' 11 In Witness whereofiwehave 'lie're'unto Setounhandsi FREDERICK 05cm :wAknzul nbomsp v. i DANIEL MACKAY- Lo'omx s.-..-:

